In Vitro Trial to Assess the Impact of Different Water Quality Parameters on the Stability of a Live Bivalent Salmonella Vaccine (Salmonella Enteritidis and Salmonella Typhimurium)

Zoonotic Salmonella strains are major pathogens causing foodborne illness, and poultry products are among the main sources of infection. Biosecurity on poultry farms is central to preventing the introduction of Salmonella; together with vaccination, it can reduce the risk of meat and eggs becoming contaminated. Live Salmonella vaccines are conveniently administered via drinking water, and good vaccination practices are essential to ensure flock protection. This requires drinking water to be compatible with live vaccines. Data about the impact of water quality on vaccine viability are limited; therefore, this study investigated the impact of different water parameters on the stability of a bivalent live Salmonella vaccine. In addition, the impact of the most common disinfectants used for drinking water sanitization was assessed. Fluoride, nitrate, sulphate levels, and hardness had little impact on vaccine survival, while aluminium, arsenic, iron, and manganese levels had a pronounced, dose-dependent effect. pH value, conductivity, and chloride levels impacted the vaccine stability only at high levels. Free chlorine, chlorine dioxide, and hydrogen peroxide strongly reduced the viability of the vaccine, even though a water stabilizer offered protection from chlorine and chlorine dioxide but not from hydrogen peroxide. These findings highlight the importance of drinking water quality for effective vaccination.